[OpenIndiana-discuss] ZFS High-Availability and Sync Replication

[Dan Swartzendruber]

I haven't had much more luck than you... 

-----Original Message-----
From: Sašo Kiselkov [mailto:skiselkov.ml at gmail.com] 
Sent: Thursday, November 15, 2012 9:07 AM
To: Discussion list for OpenIndiana
Cc: Dan Swartzendruber; zfs at lists.illumos.org
Subject: Re: [OpenIndiana-discuss] ZFS High-Availability and Sync
Replication

On 11/15/2012 12:48 PM, Dan Swartzendruber wrote:
> How sophisticated does it need to be?  I do 5-min dataset-based 
> replication to a remote pool using zrep, but that's all I use it for - a
backup...

Well, it's more of a question of mapping out the landscape of available
tools. Async replication with no automatic failover is easy enough to do
using periodic point-in-time snapshots, as you write. I was hoping there'd
be something more akin to DRBD or such like, i.e. some cluster-aware logic
behind it, something that can automatically switch over sharing services (or
something I can use to implement such an automatic switchover, such as
corosync/pacemaker), etc. In general, I've identified these possible
HA/replication scenarios:

 1) Shared-nothing nodes, i.e. separate heads & JBODs
    a) periodic async replication, run zrep/zynk/whatever every few
       minutes/seconds to send over the diffs to snapshots
    b) AVS for continuous sync/async replication

 2) Shared-storage nodes, i.e. separate heads with shared JBODs

In case 1 I need to handle two things:
  A) shipping the deltas over to the other node
  B) ensuring fail-over in case one node goes down (i.e. promote the
     slave to a master, enable file sharing services, take over IPs and
     possibly reverse the replication flow)

In case 2 I only need to handle the fail-over, as the data is the same, but
I need to handle it with very high reliability - a split brain in this case
would be catastrophic (perhaps by doing a STONITH on the other node's PDUs).

I could code this myself, but then I suspect I'd be reinventing the wheel.
This problem certainly isn't unique to myself and there's a good chance
somebody already took care of it. Sadly, though, my Google searches haven't
been very fruitful so far.

Cheers,
--
Saso